Document NEadjQ9jjV0DEeVqEZ7KXNezQ

PLAINTIFF'S EXHIBIT 4. Lynch, J.R. and H.E. Ayer Measurement of Dust Exposures in the Asbestos Textile Industry. Am. Ind. Hyg. Assoc. J. 27 (September/October 1966). 5. Edwards, R.G.etal: Dust Counting Variability. Am. Ind. Hyg. Assoc. H. 27 (November/Dec ember 1966). 6. Lynch, J.R. and J.E. Ayer Motes and Fibers in the Air of Asbestos Processing Plants and Hygienic Criteria for Airborne Asbestos. Reprint from Inhaled Particles and Vapors II (proceedings of an internal symposium organized by the British Occupational Hygiene Society). Pergamon Press, NY: 1966. 7: Crabie, J.V.: Quantitative Determination of Chyrsotile, Amosite, and Crocidolite by X-Ray Diffraction. Am. Ind. Hyg. Assoc. J. 27 (MayJune 1966). 8: Lynch. J.R. and H.E. Ayer. Measurement of Asbestos Exposure. J. of Occupational Medicine 10 (January 1968). 9. Edwards, G.H. and R. Lynch: The Method Used by the USPHS for Enumeration of Asbestos Dust on Membrane Filters. Am. Occupational Hyg. 2: 1-6 (Pergamon Press, 1968). 10. Renshaw, F.M. et al: The Use of Midget Impingers and Membrane Filters for Determining Particle Counts. Am. Ind. Hyg. Assoc. J. (March/April 1969). 11. Keenan, R.G. and J.R. Lynch: Techniques for the Detection, Identification, and Analysis of Fibers. Am. Ind. Hyg. Assoc. J. 31 (September/October 1970). 12. Lynch, J.R. et aL The Interrelationships of Selected Asbestos Exposure Indices. Am. Ind. Hyg. Assoc. J. 31 (September/October 1970). 13. Occupational Exposure to Asbestos. NIOSH (1972). USGPO SHSM72-10267. 14. LFE Corporation: Statiiticai Evaluation of the Procedure for Counting Asbestos Fibers on membrane Filters. Report submitted to the Asbestos Information Assoc, of North America, Suite 1611. 22 E. 40th St.. New York, NY 10016. 15. Symposium on Electron Microscopy of Microfibers. August 1976. USGPO 017-01200244-7. 16. Membrane Filter Method for Estimating Airborne Asbestos Dust. October 1976 Secretary. N.H. & M.R.C.. P.O. Box 100, Woden Canberra, A C T. 2606, Australia. i 17. Revised Recommended Asbestos Standard. NIOSH, December 1976. USGPO NIOSHDHEW 77-169. 18. Zumwalde, R.D. and J.M. Dement: Review and Evaluation of Analytical Methods for Environmental Studies of Fibrous Particulate Exposures. USGPO NIOSH-DHEW 77-204. May 1977. 19. Baron, P.A., Ph.D.: The Use of Light Scattering for the Detection of Filter Samples of Fibrous Aerosols. DHEW NIOSH 78-105. January 1978. 20. Levine, R.J., M.D. (editor): Asbestos: An Information Resource. DHEW NIH 79-1681. May 1978. 21. Samudra, A.V. et al: Electron Microscope Measurement of Airborne Asbestos Concentrations--A Provisional Methodology Manual. EPA 600/2-77-178. Revised June 1978. 22. Gravatt, C.C. et al: Proceedings of Workshop on Asbestos: Definitions and Measurement Methods. NBS Special Pub. Number 506, November 1978. 23. Leidel, N.A. et ai: USPHS/NIOSH Filter Method for Evaluating Airborne Asbestos Fibers. DHEW NIOSH 79-127. February 1979. Evaluation of Asbestos in Insulation DR. WALTER C. McCRONE McCrone Research Institute. Chicago, IL The Environmental Protection Agency has undertaken the coordination of a nationwide effort to eliminate a possible threat to the health of school children posed by the past use of asbestoscontaining materials in the nation's schools. The purpose, extent, and form of this effort can be best ascertained by contacting the EPA (800/424-9065; in Washington, D.C. call 554-1404). It is therefore important to have the tools and techniques available for rapid and dependable analysis of insulating, sound-proofing, and other materials used in schools for asbestiform minerals. The task of cleaning up the nation's schools makes Hercules' task of cleaning the Augean stables seem like a Sunday picnic, and the cost will be monumental. Each school and each material in each school must be considered by informed experts who can decide the best solution to the problem. Removal is very costly and could, in some cases, actually increase the hazard. Leaving well enough alone should be the recommendation unless contraindicated, for example by high friability or a high probability of disturbance. Then encapsulation (sealing in with spray finishes) or isolation (such as installing a lowered ceiling) should be considered. Each situation must, however, be considered individually. Anyone who must decide what to do must have reliable information on which to base his decision. In particular, he must know the composition of each possible asbestos-containing material. Ideally, he should know: 1. what asbestiform substances are presents; 2. in what proportion; 3. what other substances are present (e.g., cellulosic fibers, mineral wool, other glass fibers, vermiculite, talc, perlite, diatomaceous earth, organic fibers, clays, glass powder, quartz, gypsum.e tc.); and 4. size ranges for each substance. 5 398427 S IS 9 l4OGlS The third of these points is important because some of these substances are already known to be unhealthful and, the way matters are going, the others may well be declared hazardous in the future. Knowing what is present permits a more intelligent evaluation of the overall situation and may eliminate the need for a later more complete analysis. Even the chemical analytical problem is formidable and many laboratories will be involved. McCrone Associates' two laboratories in Chicago and London have analyzed thourands of samples of insulation, acoustical tile, wallboard, and other construction and decorative materials. Our staff has sampled hundreds of locations and advised many of the institutions involved as to what we think they should do based on our analyses. Finally, the McCrone Research Institute teaches the methods we feel best serve the analyst who wishes to analyze these materials. Polarized light microscopy Our method of choice is polarized light microscopy. There is. in fact, no other method capable of doing the job. Even the minimal job of detecting chrysotile, amosite, and crocidolite can only be done microscopically. Certainly the identification of ground glass, mineral wool, glass wool, diatomaceous earth, micas, clays, perlite, Lizardite, antigorite. other amphiboles. cellulosic fibers, organic fibers, etc. requires the microscope. Part of the reason is that almost the only differences between many substances are microscopic shape or optical features: e.g. lizardite, antigorite, and chrysotile: perlite, diatoms, and quartz; cotton, wood fibers, and linen; or silk, human hair, and horse hair. X-ray diffraction may help in some cases but it does not differentiate between fibrous and nonfibrous varieties of the same minerals. Furthermore, it can't identify amorphous substances such as diatoms, perlite, glass or organic fibers; nor is it useful for particle size measurement. All of these analyses are quickly accomplished microscopically. Another reason is that asbestos minerals were discovered, characterized, and named before x-ray or electron diffraction and other modem instrumental methods were invented. In fact, only chemical analysis and microscopy were then available; the differentiation of the various amphiboles and the three serptentines can only be quickly, confidently, and conclusively done by polarized light microscopy. The determination of chemical composition is not very practical on single-particles in a mixture even aside from the fact that many different substances can have identical chemical composition, e.g. riebeckite and crocidolite; grunerite or cummingtonite and amosite; lizardite or antigorite and chrysotile; fibrous and nonfibrous tremolite, fibrous and nonfibrous actinolite, or fibrous and nonfibrous ferioactinolite. Sampling The first and a major problem faced by the microscopist is sampling. Insulation, especially in microscopic samples, is far from a uniform material containing a precise percentage of fibers throughout The wide variation often found in the results from different laboratories or even the same laboratory can in most cases be explained by sample variation. The initial sample should be large enough to be representative and the microscopist must make every effort to take a representative milligram range sample. This is very difficult A sampling procedure recommended by the EPA that works very well for friable samples is to press a 35 mm film cannister completely through all layers to yield a core of material. This cannister should be carefully labeled and sent to the laboratory. There each sample should be divided in half (with careful attention to layering if present). One-half (after drying and weighing) should be placed in a small 100 ml beaker with about 50 ml of 10% Hi SO*. Only the cementicious components will dissolve, leaving the fibrous and other more inert materials in suspension. The latter can be allowed to settle for several minutes, the solution decanted, and water washed by resuspension and decantation several times. Finally, the washed particles should be resuspended by agitation to give a uniformly mixed composition. A few drops can then be removed by eyedropper and several one-drop samples can be placed on microscope slides. These, after drying, can be used for microscopical identification of the particles present. To give more quantitative results the remaining sample, after removal of the eye-dropper samples, should be filtered, dried, and weighed. This will allow calculation of the % cementicious material and, by microscopy on the residue, the percentages of the remaining components. When the budget allows, the above procedures would yield more accurate and more reproducible quantitative results. In most cases, the budget does not permit the luxury of doing such a complete job. Instead, the original ounce sample submitted to the laboratory is usually sampled at 10-20 regularly spaced locations with fine forceps, and the accumulated sample is dispersed on a microscope slide in an appropriate immersion liquid. It is the variation in composition of such samples that often leads to corresponding variations in analytical results. One should expect that repeat analyses made in this way may vary by up to 50%. Any single 1-5 mg sample often contains no asbestos in samples containing as much as 50% of that substance in the overall sample. Identification No matter how the final microscope preparation is obtained, we now have the problem of identifying each component. This is best done by classical polarized light methods together with dispersion staining, a specialized petrographic procedure. A well-trained mineralogist may not need dispersion staining although most would find it easier to apply to asbestos identification than classical optical crystallography. Any microscopist not trained in mineralogy will find dispersion staining far simpler and, indeed, the STOOliG5 I 6 6 398428 * * * m n n n n only method that can be learned in a 3-5 day course or on one's own in any reasonable time. Are asbestiform minerals present? Generally, this means--Is chrysotile, amosite (fibrous cummingtonite or grunerite). or croddolite (fibrous riebeckite) present? The actual analysis proceeds by adding a Cargille refractive index liquid (nD 1.550, high dispersion) to one of the slide samples after complete drying. The particles should be dispersed in this liquid by tearing aggregates apart, using two fine needles before covering with a coverslip. In this liquid, chrysotile has distinctive shape--very fine flexible fibrils (often curly) plus straight bundles of such fibrils--and distinctive dispersion staining colors*--usually blue-magenta parallel to the fiber axis and blue perpendicular. Different samples of chrysotile, however, may vary somewhat inJo, the wavelength at which particle and liquid have the same refractive index. Parallel to the length granges from about 440-560 nm and perpendicular to the length from about 560-660 nm.ajo for nj,-n,, is usually close to 100-120 nm. The presence of chrysotile and other fibrous particles is often obscured by a covering of large numbers of other particles. This is especially troublesome because most such particles are so different in refractive index from the mounting liquid that they appear bright white with the central stop. Trying to see the asbestos is like trying to see while driving at night with an oncoming stream of cars with high-beam headlights. Often one can be pretty sure the particles are covering obscured fibers because of their pattern. I have described this as the milky way effect. Sometimes a stray fibril may poke its way out into the liquid to show dispersion staining colors. It is always a help in such situations to examine the "milky way" with crossed polars since the underlying fibers often then become visible and recognizable as fibers. Crossed polars also help to locate smaller fibers and small percentages of fibers. Every sample should be quickly scanned with crossed polars before the absence of asbestos is reported. Amosite and crocidoiite are both very pale yellow to white by central stop dispersion staining in liquid 1.550, because their refractive indices are so much higher. Crocidoiite, of course, also usually shows a blue absorption color. If no anisotropic fibers with refractive indices much higher than 1.550 are present, the analysis is completed. If higher index anistropic fibers are present, another sample is mounted in Cargille liquid nD = 1.680 and examined with dispersion staining. Most amosites used in buildings will show a jo of about 460 nm (golden yellow) parallel to the length and about 600 nm (blue-magenta)> 660 nm (pale blue) perpendicular to the length depending on fiber orientation. A perpendicular /i* of>660 nm corresponds to the at vibration direction which usually shows oblique extinction of about 15;to 600nm perpendicular to the length corresponds \aA on the view showing parallel extinction. Higher or lower values for any one of the three vibration directions should mean higher or lower values for all three. As with most silicate minerals. substitutional solid solution--in this case Feif with Mgtr --can cause * , S , and >- to vary. Although the refractive indices of amosite and other amphiboles may vary over a wide range, most of these minerals are not from commercial sources. Nearly all amosite actually used in insulntinn commercially has the optical properties given above. If, in liquidAo'l.fiflOIow birefringent fibers show lower Xe colors close together in the yellow to golden magenta, crocidoiite is strongly indicated. If they show a negative sign ofelongation (higher ^parallel to the length) and blue absorption colors with pleochroism (blue parallel, gray-blue perpendicular), crocidoiite is present Further confirmation can be obtained by mounting a third sample in Cargille refractive index liquid O-I-70 Crocidoiite will show Po colors close to 485 nm (golden magenta) parallel to the length and about 455 (golden yellow) perpendicular. Again, some parallel movement of thea.^.ef colors should be expected for crocidolites from different sources. We should emphasize that dispersion staining is a method for rapid refractive index determination. To be certain the colors observed mean a particular asbestos is present one must be certain the dispersion staining data are consistent with particle size and shape as well as the relationship between the optical properties and the crystallographic axes. With amosite, for example, the crosswise index must be * for oblique extinction views and 6 for views showing parallel extinction. Are other asbestiform minerals present? If, during the above examination, anomalous results were observed, that is, highly fibrous with to colors in other than the prescribed ranges for chrysotile, amosite, and crocidoiite, then fibrous tremolite, fibrous actinolite, or anthophyllite may be present. These are rarely found, however, in insulation. When these anomalous results were obtained, you should have characterized the fibers in those liquids as to refractive indices relative to those liquids and extinction angles. If all of the fibers show parallel extinction, they are anthophyllite, if the possibility of organic fibers is first eliminated. Tremolite will show strong colors in all orientations in 1.605 high dispersion liquid. The oblique extinction view(ca. 15-20) will show <* perpendicular (a. ca. 440 nm; yellow) and jr nearly parallel ( ca. 680 nm; pale blue). The parallel extinction view shows /' parallel to the length (to ca. 460 nm; golden yellow) and 6 perpendicular Ue ca. 530 nm; red magenta). Actinolite has similar morphology and optics except that the indices are all higher than tremolite. Actinolite may bIbo show pleochroism (green to colorless). It is best studied in high dispersion liquid 1.630 in which * and g on the oblique extinction view show magenta (to ca. 565 nm) and golden yellow ( ca. 445 nm), respectively. On the parallel extinction view X' (lengthwise) shows ca. 470 nm or golden magenta and a (perpendicular) shows Aoca. 495 nm, also golden magenta although with more red. Tremolite, actinolite, and ferroactinolite are *The dispersion staining colors mentioned throughout this paper are those obtained by using the central stop rather than the annular. _7 398429 STQ0465I 7 r part* of a continuous solid solution series in the same manner as the amosite minerals, cummingtonite and grunierite. The name to use for a given amphibole depends directly on the optical properties, as shown in Table 1. Identification of interfering substances A few common substances show dispersion staining colors similar to those of chrysotile, and some are elongated as well. These include antigorite and lizardite (polymorphs of chryso tile), quartz, talc, paper fibers, and hairs. All of these show dispersion staining colors in 1.550 and all except talc and paper fibers show colors similar to chrysotile. Antigorite in 1.550 high dispersion liquid shows >.for * , parallel to the length, about 465 nm (golden yellow),for ot and 6 crosswise are ca. 500 nm (golden magenta) and 520 nm (redmagenta), respectively. Lizardite is platelike (often a lamellar aggregate) withA(4ca. 700 nm, pale blue) perpendicular to the plate; it generally shows undulose extinction. The6 and / indices lie in the plane of the plate and both show s near 510 nm in the 1.550 high dispersion liquid (red magenta). Quartz, although usually glassy flakes, shows blue and magenta central stop colors very similar to chrysotile in the 1.550 liquid. The shape is very different, however, and some isotropic views show only blue. Talc fibers are derived by cleavage from large talc plates; I have never seen rolled talc plated as fibers. The dispersion staining colors are therefore always very pale yellow (a#ca. 360 nm) parallel to the length. They may also show a* =360nm for the perpendicular direction but, if on edge, they will show At =645 nm (blue-green). Tapping gently on the coverslip with a needle will usually bounce these needles from the 360-360 nm view to the 360645 nm view. This is a very useful technique for quartz and other mineral grains as well. Animal and human hair may also have refractive indices in the same range as chrysotile, and if finely fibrilated, by electric razor for example, can be confusingly similar. Such fibrilated fibers are, however, rare; they also usually show melanin pigment particles and sufficiently different indices to avoid confusion. Paper fibers also show a crosswise index close to 1.55 (but lower) and the lengthwise index is much higher, hence shows a yellow color. Usually also the morphology of paper fibers is distinctive. Identification of other asbestos substitutes A number of substances are often, used as asbestos substitutes, e.g. wollastonite, glass wool, mineral wool, polyester and paper fibers. Wollastonite, a low birefringent (0.014) mineral, is triclinic and therefore shows oblique extinction in all views. It has refractive indices in the same range as tremolite and anthophyllite but, fortunately, the Q index is nearly parallel to the length, hence some views show positive and some negative signs of elongation (anthophyllite and tremolite always show a positive sign). The dispersion staining colors for wollastonite in 1.605 1'7-id are: parallel, 429 nm (yellow); perpendicular, 410 nm (pale yellow), and 532 nm (red-magenta). Glass fibers, usually as mineral wool, are often found in insulation. Different samples vary widely in refractive index and may show dispersion staining colors in any of the standard liquids from 1.55 to 1.66. Generally, however, mineral wool has low indices < 1.55, and is often coated with a colored (yellow, orange to red) resin. It is always isotropic or very slightly birefringent due to strain. Another unusual constituent found in several recent samples is a polyester fiber. The very high birefringence, uniform cylindrical crossection, and considerable length make this easy to distinguish. The indices are about 1.53 TABLE I Optical Properties of the Amphiboles Mineral Refractive indices nV Y-a Extinction Sign 2V (aver.) and e elonca'n oncic Q Treaolite 1.603-1.620 1.627-1.642 0.023 19-21 X - 86-80 Act mol It e 1.620-1.667 1.642-1.686 0.020 15-19 + - 80-70 Ferroactir.olite 1.667-1.623 1.686-1.702 0.C19 10-15 + - 70-65 Cuxningtonite - 1.633-1.664 1.654-1.687 C.022 15-21 + + 103-92 Crunente 1.664-1.636 1.687-1.729 0.033 10-15 + 92-82 Kiebeckitc 1.654-1.698 1.666-1.712 0.014 10-20 - - 40-90 Anthophyllite 1.606-1.648 1.626-1.670 0.021 0 + 68-120 8 398430 perpendicular (less than chrysoule) and 1.71 parallel (greater than crocidolite). Identification of other possible nonfibrous constituents of insulation Possible additional constituents of insulation etc. include ground glass, perlite (a heat-expanded volcanic lava), diatomaceous earth, vermiculite, and mica. Of these, ground glass, perlite, and diatoms are isotropic and characteristically shaped. Vermiculite. a clay, and the micas are very thin, flat plates often nearly isotropic but with turned-up higher birefringent edges. Vermiculite will have indices less than 1.55 and the micas above 1.55 and often above 1.605. If colored brownish-gray the mica is biotite with higher indices than colorless muscovite, another common mica. Other materials may well be found as time goes on but the observations made during the analytical procedure described above should uncover such substances, since they will not fit the data given here. All things considered, a careful microscopist. confident with dispersion staining, should have no difficulty in identifying asbestos and most other substances associated with it Acknowledgement Although fully responsible personally for the ideas expressed here, the author acknowledges with gratitude the constructive appraisal by his colleagues at McCrone Associates: John Oelly, Lucy McCrone, Mark Palenik, and Ian Stewart STOOliGS I 9 Asbestos and the Electron Microscope IAN M. STEWART Manager, Electron Optics Group, Walter C. McCrone Associates, Inc., Chicago, IL I first learned about this meeting two weeks ago, when I saw the provisional program, and my immediate reaction was that the ACGIH was going to wish on us in electron microscopy the same "raw deal," if I may call it that, as they had wished on us with light microscopy. I noted that there was to be a paper on the use of the scanning electron microscope to characterize asbestos but not one on transmission electron microscopy. I felt that this was similar to using phase contrast microscopy to tackle a mineralogical problem which is more appropriately tackled by a petrographic microscope, so I called Mr. Kelley to ask him what he was doing to us. He very kindly suggested that I come along and present my views in the general discussion at this meeting and so I came prepared with one or two slides to do this. When I arrived, however, Jim Ferguson told me that I was to present my views a little more formally, so here they are. Criteria for Asbestos identification Let me say from the outaet that I should not be regarded as an anti-scanning electron microscope man. There are many stiuations in which the scaning electron microscope is the appropriate tool to use, but I do not believe that the asbestos situation is necessarily one of them. My reasons for saying this are that, like Dr. McCrone, 1 believe that the main criteria by which one must identify asbestos are crystallographic with chemistry as a secondary consideration, and the scaninng electron microscope is unfortunatly lacking in its ability to give crystallographic characterization from particles of the sizes which are going to be of interest to us. An additional problem in many scanning electron microscopes is that of resolution. Although manufacturers currently will claim that resolutions are better than 100 A (lOnm) for their microscopes, they do reserve the right to select the specimens on which they demonstrate this resolution, and their samples are generally those with very clearly defined features and very high contrast. This situation does not normally prevail with asbestos fibers down to unit fibril dimensions. Having brought in the term "unit fibril," let me define it. This term is applied generally to chrysotile asbestos. It is the smallest chrysotile fiber which can exist as a single entity and has an approximate diameter of 300-350 A (30-35 nm). Fibers of these dimensions are quite common in environmental samples but one does generally see larger fibers in the workplace. However, as control procedures improve, it is to be hoped that the larger fibers will be less prevalent in the workplace, in which case we will have to concentrate on the very fine fibers which are not visible and thus cannot be characterized by the light microscope. How then do we go about characterizing these fine fibrils with the electron microscope? As I have mentioned, the principal criterion is a crystallographic one. However, one may summarize the three main criteria for identification of a fiber as asbestos under three headings: morphology, crystallography, and chemistry. Morphology Clearly, since you are interested in controlling asbestos fibers, the particle in question must have the morphology of a fiber. I will not at the present time go into the various semantics of defining a fiber. But I will say that, at this time, everyone concerned with this problem is utilizing (I almost said accepting) the federal definition of a fiber as a particle with an aspect ratio greater than 3:1. It is quite possible that this may stimulate some discussion. However, though one may argue the semantics of a fiber from a mineralogist's point of view, the final criterion to decide what will be called a fiber for regulatory purposes must only be the biological significance of the particles's aspect ratio. This is a subject on which I am not qualified 9 I 398431 0Z 9 J1001S C ASBESTOS 2 fibers longer than S pm per cc. for chrysotile 0.2 fibers longer than S pa per cc. for crocidolite 0.S fibers longer than S pm per cc. for amosite According to recent authoritative mineralogical definitions, ^ ^ asbestos is "(1) A collective mineralogical term encompassing the asbestiform varieties of various minerals; (2) An industrial product obtained by mining and processing primarily asbestiform minerals." For the purpose of considering a recommendation for a threshold value of asbestos dust in the workplace, only the second definition above is applicable. Although there are four types of natural mineral fibers that have been in industrial use, only three have been used in the United States: chrysotile, amosite, and crocidolite. The fourth, anthophyllite, is mined and used in Finland. Of the three types of asbestos that have been used in North America, Canadian chrysotile has formed 95* of all natural mineral fibers used, with amosite and crocidolite (both imported from South Africa) constituting the other S*. It should be noted that chrysotile is classified as a serpentine mineral whereas the other three types of asbestos are amphiboles. It is now generally recognized that excessive inhalation of asbestos dust causes chronic inflammations of lung tissue and pleural membranes as well as cancers. Whereas identification of asbestos dust as a cause of fibrosing inflammation of lung tissue occurred as early as 1907, J it^was not until 1930 that a more definitive study by Merewether and Price ^ resulted in the regulations which greatly improved hygenic conditions in asbestos factories in the United kingdom. The development of lung cancer in asbestos workers, first reported by Wood and Gloyne^ ` in the U.K. in 1934 and by Lynch and Smith^ "in the U.S. in,193S, was not firmly estab lished until 19SS by the publication of Doll^ ' of a study of workers in an English asbestos textile factory, and in the United States by the paper of Selikoff et al^/J in 1964 concerned with cancers in insulation workers. In 1960 the relationship between the inhalation of asbestos dust and meso thelioma was demonstrated by Wagner et al. ` Asbestosis is a diffuse but nonuniform fibrosis of the lungs that is generally most severe in the basilar portions. As a result of the fibro sis some of the air-spaces (alveoli) are not perfused with blood and al veoli that are perfused with blood may not be adequately ventilated because of stiff, thickened alveolar walls. The fibrosis makes the lungs less com pliant, thereby increasing the energy requirement of breathing. There is increasing impairment in diffusion of gases leading to increasing breath lessness. It is not uncommon to find thickening of the visceral pleura, some times very severe, by extension of the parenchymal inflammation. This causes an additional increase in the effort of breathing. 398432 ST00I.652I The parietal pleura nay show patches of severe thickening, particular ly over the diaphragm and the lower portions of the chest wall - resulting in the so-called pleural hyaline plaques. These may become visible in X-ray films of the chest - particularly, if they become impregnated with calcium salts. Such pleural plaques may develop from asbestos exposure in the absence of asbestosis. They cause no symptoms. A study of the members of an asbestos insulators union revealed that f7^ deaths from lung cancer in this population was much greater than expected: A later investigation by Hammond and Selikoff of a much larger number of these workers (.17,800) showed that nearly all cancers occurred in cigarette smokers. The conclusion of these authors was, "It seems clear, then, that lung cancer is uncommon among asbestos insulation workers who have no history of cigarette smoking, and that if the risk is increased such an increase is not great." The total lung cancer rate in this cohort of workers was 4.8 times the ex pected. The asbestos insulators who had a history of cigarette smoking had a lung cancer rate 5.4 times the expected rate; but compared to the lung cancer rate of the nonsmoking workers, the smoking insulators' lung cancer rate was 14 times greater. All types of asbestos are known to cause the inflammatory changes in the lungs and pleurae described above and lung cancer. However, there is experimental and epidemiologic evidence that there may be differences in the potential of the different asbestos types of produce disease. Thus, it has been suggested that crocidolite has the greatest potential to pro duce disease; chrysotile, the smallest; with amosite occupying an inter mediate position. ' In a study,of.1348 retirees from the asbestos in dustry by Enterline and Henderson^ ' the respiratory cancer rate of men exposed only to chrysotile was 2.4 times the expected, whereas this rate was 5.3 times the expected for men who had been exposed to a combination of chrysotile and crocidolite. In the asbestos cement industry a similar difference was observed. Workers exposed only to chrysotile and cement (shingles and sheets) had a respiratory cancer rate of 1.4 times the ex pected, whereas workers exposed to both, chrysotile and crocidolite and cement (asbestos cement pipes), had a respiratory cancer rate 6.1 times the expected. Mesotheliomas are rare, usually rapidly fatal cancers that originate from the surface lining the chest or abdominal cavity..From I960 through 1975, 4539 mesotheliomas have been reported worldwide. ' The vase major ity of these cancers were in people exposed to crocidolite alone.or in combination with other types of asbestos. McDonald and McDonald^ ' tabu lated those reports of mesothelioma where the type of asbestos exposure was known. Although the number of such cases is small, where the exposure was to crocidolite alone or in combination with other type of asbestos, death from mesothelioma constituted 6.1% of the deaths from all causes, with a range of 2.42% to 16.07% In contrast, deaths from mesothelioma in workers exposed only to chrysotile constitued only 0.3% of the deaths from all causes, with a range of 0.24% to 0.87%. An even greater contrast is found in the Finnish statistics of workers exposed to anthophyllite. Meurman et al^ J investigated 216 deaths that occurred among approximately 900 miners and millers of anthophyllite during the 32-year period 1936-1967 and found not one case of mesothelioma. 398433 2 2 5 9 'iO O iS Not all mesotheliomas result from asbestos exposure. There is a back ground of "naturally'' occurring mesotheliomas that has been estimated to be about ten for males and four for females per million persons aged 45 years and older.1 i Furthermore, it is not uncommon in the various epidemiologic studies reported that 15% or more of the mesothe lioma cases have no history of ever having been exposed to asbestos. Perhaps the most important indication that mesotheliomas may result from causes other than asbestos exposures; in this.instance, also environmental, comes from a report by Baris et al ^ Jwho described a mesothelioma incidence of 2. 3% in 1974 in the village of Karain in Turkey ^population, 604). This population has been exposed for many generations to dust from the soil that contains kaolin, mica, and vulcanic glass particles, but no asbestos. A small excess of deaths from gastro-intestinal cancers have been noted in several epidemiologic studies of asbestos workers.^ ' * An association of laryngeal cancer with asbestos exposure has been claimed. Pancreatic cancers and lymphomas have also been mentioned in this connection. However, conversion of the association to a causal relation ship rests as yet on an insecure basis. Whether or not there is a dose-effect relationship associated with asbestos ,^\istghas been answered affirmatively by a number of epidemiological surveys. * ^Whereas this relationship is clear-cut with regard to (asbestosis and lung cancer, it is less well-marked with regard to) mesothelioma; but it is, nevertheless positive. McDonald ^ "points to a case-control analysis based on seven cases of mesothelioma at Thetford Mines that includes no case with less than 30 mppcf years exposure and which suggests that the risk increases with exposure. McDonald further points out that although fiber-equivalents for the dust concentrations in mppcf are difficult to estimate, there is evidence for believing that the conversion factor cannot be less than two. The data of Newhouse and Berry ^ ' demonstrates a doubling of the incidence of mesothelioma for males who had severe exposures as compared to that of the workers who had light or moderate exposures. This was equally true for those employed less than two years. In all of the other investigations of mesothelioma incidence, the degree of dust exposure was not indicated, thereby preventing the determina tion of any dose effect relationship. The only reliable exposure data from the asbestos industry on which a recommendation for a threshold.limit of asbestos exposure can be based, stem from England. * ' J Using the presence of persistent high-pitched rales in the basal portions of the lungs as criterion for the diagnosis of asbestosis, it was determined from a population of asbestos textile workers that less than 100 fiber-years of exposure (2 fibers per cc. over a 50 year working period or 4 fibers per cc. over a 25 year period would cause.the development of asbestosis in no more than 1% of the workers. ' This departure from the previous dust standard of 5 mppcf was in recognition of the variability of the asbestos fiber content of factory dust and that the disease was ^elated to the number of asbestos fibers inhaled and not to the amount of nonfibrous dust particles. Also, it was specified that the counted fibers were to be longer than 5 um. 398434 ST0046523 The size limit placed on the counted fibers (longer than 5 pm) was because it was not practical to count shorter fibers with an optical microscope (400 to JO x magnification under phase-contrast illumination, with a 4W. objective). It is recognized that for every asbestos fiber longer than S pm, there may be as many as 100 or more fibers shorter and thinner that are not visible under the optical microscope. However, there is considerable experimental evidence to.indicate that asbestos fibers shorter than S um are not pathogenic.1 A recent publication by Gillam et al('24) indicated that the present limit of 2 asbestos fibers per cc. longer than 5 pm set by OSHA is in adequate to protect workers against nonmalignant as well as malignant respiratory disease. This conclusion was based on a study of 440 hard rock gold miners who had been exposed to an asbestiform mineral (cummingtonite-grunerite). These investigators found 10 respiratory cancer deaths (including a carcinoma of the maxillary sinus and a mediastinal carcinoma) when only 2.74 such deaths had been expected. Five deaths from nonmalignant respiratory diseases other than influenza and pneumonia when 1.85 deathsfrom these causes had been expected. These deaths included those from silicosis (the respirable dust contained 13% free silica!). It is of interest that although the.diagnosis of asbestosis was not mentioned in the paper, Gillam et ar ' emphasized the finding that the ambient air in the gold mine contained an average of 4.82 fibers per cc., 80 to 90% of which were fibrous amphiboles, "and 60 to 70% of the latter were fibrous grunerite (amosite)." Fibers longer than S um, averaged 0.36 fibers per cc.; and approximately 94% of the airborne fibers were less than 5 um long, averaging 0.13 in diameter and 1.1 pm in lengths. McDonald et al^25^ investigated the records of the same gold mine as Gillam et al but their cohort consisted of 1321 men who had completed 21 years service with the mining.company (in contrast to the cohort of 440 men studied by Gillam et al1 . The following is a summary of their findings: "All but 10 of the men were traced to the end of 1973 when 651 were still living; cause of death was ascertained for 657 of the 660 who had died. The numbers of deaths observed in various diagnostic categories, with 'expected' figures in parenthesis, were as follows: - respiratory cancer - 17 (16.5); abdominal cancer - 39 (35.1); other malignant diseases - 37 (39.0); pneumoconioses - 39 (0); respiratory tuberculosis or silicotuberculosis - 39 (3.6); heart disease - 264 (232.5). Silicosis was given as the cause in 37 of the 39 pneumoconiotic deaths and mentioned on the certificate in 28 of the 264 coded to heart disease. The occurrence of deaths ascribed to pneumoconiosis, tuberculosis and heart disease was in each case related directly to dust-exposure category whereas deaths coded to respiratory, abdominal and other cancers showed no such relationship. The pattern of mortality of men with long employment in this industry in dicates a serious pneumoconiotic hazard characteristic of hard rock miners but not of cancer." (See Table 1.) 398435 las^ioois It would appear from the McDonald et,al.study^ that there is no basis for the claim made by Gillam et al1 ' that the OSHA standard of two fibers longer than 5 urn per cc. is inadequate to protect the health of workers, or that asbestos fibers shorter than 5 pi produce deleteri ous health effects. In an 85j year follow-up of the same population of asbestos workers from which the 100 fiber-years exposure was derived as a reasonablyQsafe level, it was found that mortality was increased for lung cancer. ' There were 31 deaths from this cause whereas only 19.3 had been expected. From non malignant respiratory disease, there were 35 deaths where 25.0 had been expected. In addition, there were five deaths from pleural mesothelioma. It was determined that the mean dust level of the workers had been below five fibers per cc. only in the last decade. In 1951 the mean dust level was 10.8 fibers per cc. and 89% of the men had been exposed to mean levels above 5 fibers per cc. In 1972, the mean dust level was 2.9 fibers per cc. and only 3% of the men were exposed to a mean level greater than 5 fibers per cc., 65% were exposed to a mean level between two and five fibers per cc. and 32% to a mean level below 2 fibers per cc. Because there is a delay of 15 or more years between first exposure and any resulting cancer, the authors consider that the increased mortali ty demonstrated does not reflect the effects of working conditions over the last 15 or 20 years. They therefore propose to continue the follow-up on workers entering scheduled areas since 1951. In terms of the 100 fiber-year or two fibers per cc. standard suggested by the British Occupa tional Hygiene Society [B.O.H.S.), it is apparent that the excess mortality reported above can be attributed to asbestos exposures considerably above this level. The workers in the asbestos textile factory from which the B-0.H.5. standard of 2 fibers per cc. was derived have been studied by highly.quali fied investigators whose reports were published in 1955, ' 1965, 1968, and 1977. These workers represent the only cohort of asbes tos workers in the world in which health effects have been correlated with definitive exposure data defined as fibers per cc. It would be premature and ill advised to change the present OSHA standard of 2 fibers longer than 5 urn per cc. for chrysotile without indications from this study population of the advisability for such change. The exposure level of crocidolite and amosite, particularly of the former, must be sharply lower than that of chrysotile because of their greater potential for disease production. In view of the lack of accurate information of the dose-effect relationship pertaining to these two types of asbestos, the arbitrary assignment of 0.2 fiber per cc. longer than 5 um appears reasonable and prudent for both, crocidolite and amosite, even though amosite may be less pathogenic than crocidolite. 398436